Human term placental alkaline phosphatase (PLAP) is an enzyme produced by the syncytiotrophoblast from the 12th week of pregnancy on. It shows a high degree of genetic polymorphism as disclosed by electrophoretic analysis. A PLAP-like enzyme is expressed in normal human testis which does not display the electrophoretic polymorphism of PLAP and differs from PLAP in its sensitivity to inhibition by certain amino acids and peptides and in its reactivity with monoclonal antibodies. These data suggest that PLAP and PLAP-like isozymes represent different structural proteins and so could be products of different genes. The purpose of this application is to test this hypothesis at the gene level. We will sequence a full-length PLAP cDNA clone and characterize salient features of the inferred amino acid sequence. We will isolate and characterize a full-lenth PLAP-like cDNA clone from a testis Lambdagt11 cDNA expression library. The amino acid sequence of the protein will be inferred from the DNA data and compared to the primary structure of PLAP. Monoclonal antibodies and DNA probes specific for PLAP and PLAP-like enzymes will be generated exploiting these structural differences of the proteins as inferred for the DNA sequence. These reagents will allow the study of different structural and functional domains in the molecules, the investigation of the expression and regulation of PLAP and PLAP-like enzymes and their allelic variants, and will improve the clinical quantitation and application of these enzymes. We will isolate and characterize genomic DNA clones encompassing the genes for PLAP and PLAP-like enzymes. PLAP and PLAP-like enzymes are ofen found in the sera, fluids, and tumor tissues of cancer patients where they can be measured as markers of malignancy. The use of these enzymes as tumor markers and as possible targets for antibody therapy of cancer would greatly benefit from a more precise knowledge of the molecules and the genetic basis of their differences.